The present invention relates to a gas transfer duct, and particularly to a gas transfer duct having a heat-insulating effect and a sound-absorbing effect suitable for transferring air-conditioning air which is set to have temperature different from room temperature.
Such a conventional gas transfer duct generally has a structure in which heat-insulating foamed material is spirally wound around an outer circumferential surface of a duct body with no space, a thin film-like resin tape is wound around an outer circumferential of the heat-insulating foamed material and the duct body defines an inner circumferential surface of the duct.
In such a conventional duct having a structure in which a duct body defines an inner circumferential surface of the duct, the duct becomes a guide cylinder through which noise generated from an air-blow source such as an air blower is guided to an opening portion of the duct while gas is transferred. The noise is discharged together with the gas, to thereby give people an unpleasant feeling. There has been a problem that such noise jars on people's nerves because it is generated continuously while the duct is in use, that is, in air-blowing operation.
In order to solve the above-mentioned problem belonging to air-blow ducts of the conventional type, that is, to largely reduce such the unpleasant noise discharged from the opening of the duct though it may be impossible to entirely extinguish such an unpleasant noise, there has been developed and proposed a structure which is taught by Japanese patent unexamined publication No. Hei. 9-89357. In structure, woven cloth having predetermined width is wound spirally, and then, connection edges of the cloths thus wound are bonded to each other with strip-shaped hard resin material, so that an internal surface layer of a duct is defined. A foam strip of open cells is spirally wound on an outer circumferential surface of the woven cloth while adjacent side edges of the adjacent foam strips are brought into contact with each other, so that an open-cell foam layer is formed. A thin film sheet-like strip is spirally wound on an outer circumferential surface of the open-cell foam so as to form an intermediate sheet layer. A foam strip of closed-cell foam is spirally wound on an outer circumferential surface of the intermediate sheet layer so as to form a closed-cell foam layer. A resin tape is spirally wound on an outer circumference of the closed-cell foam so as to form an external surface layer which wraps the outermost circumference thereof.
This air-blow duct is a product having a superior effect to be able to show substantially practically perfect effects of noise-reducing and heat-insulating functions as expected. The duct is therefore an ideal and suitable product for use as an air-blow duct. This product has, however, only one problem that the manufacturing process is complicated and its cost is not satisfied.